There is a cup that separates the injector from the head.  It has been problematic in that the seals fail and allow fuel into the coolant.  If they haven't been replaced it is only a matter of time.  Not a terrible job, but takes several hours and a special tool.  If the gudgeon has bushings they will fail.  The replacement will have bearings and is a much better system.  Requires separating tractor to replace and is an expensive part.  Look for metal filings around the pivot point.  If it is left go too long it will be a major repair expense.  I once saw one that had been ignored so long the tractor had a noticeable swayback from the wear.  High hours wear out the isolators for the cab which makes it noticeably louder.  Easy to replace.